Total Synthesis of Vibrio Cholerae O43 Tetrasaccharide Repeating Unit

Vibrio cholerae is a pathogen responsible for the deadly pandemic - cholera. The glycans present on the surface of various strains of V. cholerae are considered as potential vaccine candidates. The tetrasaccharide repeating unit (RU) of V. cholerae O43 is decorated with less-explored rare deoxy amino sugars like d-quinosamine and d-viosamine, along with a rare amino acid, N-acetyl-l-allothreonine. Herein, we report a detailed account of the total synthesis of V. cholerae O43 tetrasaccharide RU. In our earlier attempt, while a one-pot assembly of trisaccharide was successful, the final coupling with a fully functionalized d-viosamine donor was low yielding. The successful route involved employing the Fmoc-protected d-viosamine building block as a donor and a late-stage amide bond formation of the tetrasaccharide.

Elucidating liquid crystal-aqueous interface for the study of cholesterol-mediated action of a β-barrel pore forming toxin

Pore-forming toxins (PFTs) produced by pathogenic bacteria serve as prominent virulence factors with potent cell-killing activity. Most of the β-barrel PFTs form transmembrane oligomeric pores in the membrane lipid bilayer in the presence of cholesterol. The pore-formation mechanisms of the PFTs highlight well-orchestrated regulated events in the membrane environment, which involve dramatic changes in the protein structure and organization. Also, concerted crosstalk between protein and membrane lipid components appears to play crucial roles in the process. Membrane-damaging lesions formed by the pore assembly of the PFTs would also be expected to impose drastic alterations in the membrane organization, details of which remain obscure in most of the cases. Prior reports have established that aqueous interfaces of liquid crystals (LCs) offer promise as responsive interfaces for biomolecular events (at physiologically relevant concentrations), which can be visualized as optical signals. Inspired by this, herein, we sought to understand the lipid membrane interactions of a β-barrel PFT i.e., Vibrio cholerae cytolysin (VCC), using LC-aqueous interfaces. Our results show the formation of dendritic patterns upon the addition of VCC to the lipid embedded with cholesterol over the LC film. In contrast, we did not observe any LC reorientation upon the addition of VCC to the lipid-laden LC-aqueous interface in the absence of cholesterol. An array of techniques such as polarizing optical microscopy (POM), atomic force microscopy (AFM), and fluorescence measurements were utilized to decipher the LC response to the lipid interactions of VCC occurring at these interfaces. Altogether, the results obtained from our study provide a novel platform to explore the mechanistic aspects of the protein-membrane interactions, in the process of membrane pore-formation by the membrane-damaging PFTs.

Fragmentation analysis of O-specific polysaccharide from bacteria Vibrio cholerae O139 by MALDI-TOF and LC/ESI-MS/MS

Cholera is a life-threatening diarrhoeal disease caused by ingestion of Vibrio cholerae. There are at least 200 serogroups of V. cholerae but only two of them are causing epidemics - O1 and O139 serogroups. Fragmentation analysis of O-antigen, also known as O-specific polysaccharide (OSP), from lipopolysaccharide (LPS) is important to obtain new information about its structure, such as fragmentation patterns and fragment structures. In the present study, OSP and core (OSPc) structure from V. cholerae O139 was studied using matrix-assisted laser desorption ionization (MALDI)-time of flight (TOF) and direct injection electrospray ionization (ESI)-MS methods. MALDI-TOF analysis was performed in positive-ion reflectron mode, while ESI-MS was performed in negative ionization mode. ESI-MS analysis was followed by ESI-MS/MS analysis. Using this analytical approach, we managed to obtain two possible fragmentation pathways of OSP from V. cholerae O139. Mutual sign of these two pathways is shortening the length of the oligosaccharide by neutral loss of monosaccharide residues. Additionally, liquid chromatography-MS analysis was performed to separate depicted molecular forms of OSPc.

A mutagenic screen reveals NspS residues important for regulation of Vibrio cholerae biofilm formation

Biofilm formation in the human intestinal pathogen Vibrio cholerae is in part regulated by norspermidine, spermidine and spermine. V. cholerae senses these polyamines through a signalling pathway consisting of the periplasmic protein, NspS, and the integral membrane c-di-GMP phosphodiesterase MbaA. NspS and MbaA belong to a proposed class of novel signalling systems composed of periplasmic ligand-binding proteins and membrane-bound c-di-GMP phosphodiesterases containing both GGDEF and EAL domains. In this signal transduction pathway, NspS is hypothesized to interact with MbaA in the periplasm to regulate its phosphodiesterase activity. Polyamine binding to NspS likely alters this interaction, leading to the activation or inhibition of biofilm formation depending on the polyamine. The purpose of this study was to determine the amino acids important for NspS function. We performed random mutagenesis of the nspS gene, identified mutant clones deficient in biofilm formation, determined their responsiveness to norspermidine and mapped the location of these residues onto NspS homology models. Single mutants clustered on two lobes of the NspS model, but the majority were found on a single lobe that appeared to be more mobile upon norspermidine binding. We also identified residues in the putative ligand-binding site that may be important for norspermidine binding and interactions with MbaA. Ultimately, our results provide new insights into this novel signalling pathway in V. cholerae and highlight differences between periplasmic binding proteins involved in transport versus signal transduction.

Janus Micromotors Coated with 2D Nanomaterials as Dynamic Interfaces for (Bio)-Sensing

In this work, we study the interaction of graphdiyne oxide (GDYO)-, graphene oxide (GO)-, or black phosphorous (BP)-wrapped Janus micromotors using a model system relying on a fluorescence-labeled affinity peptide, which is released upon specific interaction with a target Cholera Toxin B. Such ON-OFF-ON system allows mimicking similar processes occurring at (bio)-interfaces and to study the related sorption and desorption kinetics. The distinct surface properties of each nanomaterial play a critical role in the loading/release capacity of the peptide, greatly influencing the release profiles. Sorption obeys a second-order kinetic model using the two-dimensional (2D) nanomaterials in connection with micromotors, indicating a strong influence of chemisorption process for BP micromotors. Yet, release kinetics are faster for GDYO and GO nanomaterials, indicating a contribution of π and hydrophobic interactions in the probe sorption (Cholera Toxin B affinity peptide) and target probe release (in the presence of Cholera Toxin B). Micromotor movement also plays a critical role in such processes, allowing for efficient operation in low raw sample volumes, where the high protein content can diminish probe loading/release, affecting the overall performance. The loading/release capacity and feasibility of the (bio)-sensing protocol are illustrated in Vibrio cholerae and Vibrio parahaemolyticus bacteria cultures as realistic domains. The new concept described here holds considerable promise to understand the interaction of micromotor with biological counterparts in a myriad of biomedical and other practical applications, including the design of novel micromotor-based sensors.

Enzymatic Syntheses and Applications of Fluorescent Cyclic Dinucleotides

Bacterial cyclic dinucleotides (CDNs) play important roles in regulating biofilm formation, motility and virulence. In eukaryotic cells, theses bacterial CDNs are recognized as pathogen-associated molecular patterns (PAMPs) and trigger an innate immune response. We report the photophysical analyses of a novel group of enzymatically synthesized emissive CDN analogues comprised of two families of isomorphic ribonucleotides. The highly favorable photophysical features of the CDN analogues, when compared to their non-emissive natural counterparts, are used to monitor in real time the dinucleotide cyclase-mediated synthesis and phosphodiesterase (PDE)-mediated hydrolysis of homodimeric and mixed CDNs, providing effective means to probe the activities of two classes of bacterial enzymes and insight into their biomolecular recognition and catalytic features.

Structural insights into the mechanism of oxidative activation of heme-free H-NOX from Vibrio cholerae

Bacterial heme nitric oxide/oxygen (H-NOX) domains are nitric oxide (NO) or oxygen sensors. This activity is mediated through binding of the ligand to a heme cofactor. However, H-NOX from Vibrio cholerae (Vc H-NOX) can be easily purified in a heme-free state that is capable of reversibly responding to oxidation, suggesting a heme-independent function as a redox sensor. This occurs by oxidation of Cys residues at a zinc-binding site conserved in a subset of H-NOX homologs. Remarkably, zinc is not lost from the protein upon oxidation, although its ligation environment is significantly altered. Using a combination of computational and experimental approaches, we have characterized localized structural changes that accompany the formation of specific disulfide bonds between Cys residues upon oxidation. Furthermore, the larger-scale structural changes accompanying oxidation appear to mimic those changes observed upon NO binding to the heme-bound form. Thus, Vc H-NOX and its homologs may act as both redox and NO sensors by completely separate mechanisms.

Designing an Outer Membrane Protein (Omp-W) Based Vaccine for Immunization against Vibrio and Salmonella: An in silico Approach

BACKGROUND

Cholera triggered by Vibrio cholerae remains the main reason for morbidity and mortality all over the world. In addition, salmonellosis is regarded as an infectious disease that makes it essential for the identification and detection of Salmonella. With a beta-barrel structure consisting of eight non-parallel beta strands, OmpW family is widely distributed among gram-negative bacteria. Moreover, OmpW isolated from S. typhimurium and Vibrio cholerae can be used in vaccine design.

METHODS

Topology prediction was determined. T-cell and B-cell epitopes were selected from exposed areas, and sequence conservancy was evaluated. The remaining loops and inaccessible residues were removed to prepare OmpW-1. High antigenicity peptides were detected to replace inappropriate residues to obtain OmpW-2. Physicochemical properties were assessed, and antigenicity, hydrophobicity, flexibility, and accessibility were compared to the native Omp-W structure. Low score areas were removed from the designed structure for preparing the OmpW-3. To construct OmpW-4, TTFrC was used as T-CD4+ cell-stimulating factor and CTB as adjuvant to the end of the C-terminal of this sequence, which can increase the antigenicity and sequence density. The sequences were re-analyzed to delete the unfavorable residues. Besides, the solubility of the mature OmpW and the designed structure were predicted while overexpressed in E. coli.

RESULTS

The designed vaccine is a stable protein that has immune cells recognizing epitopes and is considered as an antigen. The construct can be overexpressed in an E. coli.

CONCLUSION

The multi-epitope vaccine is a suitable stimulator for the immune system and would be a candidate for experimental research. Recent patents describe numerous inventions related to the clinical facets of vaccine peptide against human infectious disease.

Direct Conjugation of Bacterial Polysaccharides to Proteins by Squaric Acid Chemistry

Bacterial polysaccharides that contain one amino group can be conjugated using squaric acid chemistry directly to a protein carrier. The conjugation is a two-step process consisting of labeling the polysaccharide with a squarate group and a reaction of the squarate formed with protein. The intermediate squarate derivative and the product glycoconjugate can be easily purified using centrifugal filtration devices. This method is experimentally simple and affords glycoconjugates with predictable carbohydrate-protein ratio (carbohydrate content), high conjugation efficiency, and excellent yield.

Structure elucidation and gene cluster annotation of the O-antigen of Vibrio cholerae O100 containing two rarely occurred amino sugar derivatives

O-polysaccharide (O-antigen) was isolated from the lipopolysaccharide of Vibrio cholerae O100 and studied by component analyses and 1D and 2D NMR spectroscopy. The following structure of the O-polysaccharide was established: →3)-β-d-QuipNAc4N(dHh)-(1 → 3)-α-d-Fucp4N(RHb)-(1 → 3)-α-l-FucpNAc-(1→ where Hb and dHh indicate 3-hydroxybutanoyl and 3,5-dihydroxyhexanoyl, respectively. The O-antigen gene cluster of V. cholerae O100 has been sequenced. The gene functions were tentatively assigned by comparison with sequences in the available databases and found to be in agreement with the OPS structure.

Structure of the GH9 glucosidase/glucosaminidase from Vibrio cholerae

Glycoside hydrolase family 9 (GH9) of carbohydrate-processing enzymes primarily consists of inverting endoglucanases. A subgroup of GH9 enzymes are believed to act as exo-glucosidases or exo-glucosaminidases, with many being found in organisms of the family Vibrionaceae, where they are proposed to function within the chitin-catabolism pathway. Here, it is shown that the GH9 enzyme from the pathogen Vibrio cholerae (hereafter referred to as VC0615) is active on both chitosan-derived and β-glucoside substrates. The structure of VC0615 at 3.17 Å resolution is reported from a crystal form with poor diffraction and lattice disorder. VC0615 was highly refractory to crystallization efforts, with crystals only appearing using a high protein concentration under conditions containing the precipitant poly-γ-glutamic acid (PGA). The structure is highly mobile within the crystal lattice, which is likely to reflect steric clashes between symmetry molecules which destabilize crystal packing. The overall tertiary structure of VC0615 is well resolved even at 3.17 Å resolution, which has allowed the structural basis for the exo-glucosidase/glucosaminidase activity of this enzyme to be investigated.

Identification of a Small Molecule Activator for AphB, a LysR-Type Virulence Transcriptional Regulator in Vibrio cholerae

AphB is a LysR-type transcriptional regulator (LTTR) that cooperates with a second transcriptional activator, AphA, at the tcpPH promoter to initiate expression of the virulence cascade in Vibrio cholerae. Because it is not yet known whether AphB responds to a natural ligand in V. cholerae that influences its ability to activate transcription, we used a computational approach to identify small molecules that influence its activity. In silico docking was used to identify potential ligands for AphB, and saturation transfer difference nuclear magnetic resonance was subsequently employed to access the validity of promising targets. We identified a small molecule, BP-15, that specifically binds the C-terminal regulatory domain of AphB and increases its activity. Interestingly, molecular docking predicts that BP-15 does not bind in the putative primary effector-binding pocket located at the interface of RD-I and RD-II as in other LTTRs, but rather at the dimerization interface. The information gained in this study helps us to further understand the mechanism by which transcriptional activation by AphB is regulated by suggesting that AphB has a secondary ligand binding site, as observed in other LTTRs. This study also lays the groundwork for the future design of inhibitory molecules to block the V. cholerae virulence cascade, thereby preventing the devastating symptoms of cholera infection.

USE OF VIBRIO CHOLERAE SURFACE STRUCTURES FOR SPECIFIC PROPHY- LAXIS AND DIAGNOSTICS OF CHOLERA

The need for efficient and cost-effective cholera vaccine hasn't lost its actuality in view of the emergence of new strains leading to severe clinical forms of cholera and capable to replace strains of the seventh.cholera pandemic, and in connection with the threat of cholera spreading beyond the borders of endemic countries. In this review data from literature sources are presented about the use of outer membrane proteins, vesicles, cell ghosts of the cholera causative agent in specific prophylaxis and diagnostics of the disease.

Structural and biochemical studies on Vibrio cholerae Hsp31 reveals a novel dimeric form and Glutathione-independent Glyoxalase activity

Vibrio cholerae experiences a highly hostile environment at human intestine which triggers the induction of various heat shock genes. The hchA gene product of V. cholerae O395, referred to a hypothetical intracellular protease/amidase VcHsp31, is one such stress-inducible homodimeric protein. Our current study demonstrates that VcHsp31 is endowed with molecular chaperone, amidopeptidase and robust methylglyoxalase activities. Through site directed mutagenesis coupled with biochemical assays on VcHsp31, we have confirmed the role of residues in the vicinity of the active site towards amidopeptidase and methylglyoxalase activities. VcHsp31 suppresses the aggregation of insulin in vitro in a dose dependent manner. Through crystal structures of VcHsp31 and its mutants, grown at various temperatures, we demonstrate that VcHsp31 acquires two (Type-I and Type-II) dimeric forms. Type-I dimer is similar to EcHsp31 where two VcHsp31 monomers associate in eclipsed manner through several intersubunit hydrogen bonds involving their P-domains. Type-II dimer is a novel dimeric organization, where some of the intersubunit hydrogen bonds are abrogated and each monomer swings out in the opposite directions centering at their P-domains, like twisting of wet cloth. Normal mode analysis (NMA) of Type-I dimer shows similar movement of the individual monomers. Upon swinging, a dimeric surface of ~400Ų, mostly hydrophobic in nature, is uncovered which might bind partially unfolded protein substrates. We propose that, in solution, VcHsp31 remains as an equilibrium mixture of both the dimers. With increase in temperature, transformation to Type-II form having more exposed hydrophobic surface, occurs progressively accounting for the temperature dependent increase of chaperone activity of VcHsp31.

Unraveling the stereochemical and dynamic aspects of the catalytic site of bacterial peptidyl-tRNA hydrolase

Bacterial peptidyl-tRNA hydrolase (Pth; EC 3.1.1.29) hydrolyzes the peptidyl-tRNAs accumulated in the cytoplasm and thereby prevents cell death by alleviating tRNA starvation. X-ray and NMR studies of Vibrio cholerae Pth (VcPth) and mutants of its key residues involved in catalysis show that the activity and selectivity of the protein depends on the stereochemistry and dynamics of residues H24, D97, N118, and N14. D97-H24 interaction is critical for activity because it increases the nucleophilicity of H24. The N118 and N14 have orthogonally competing interactions with H24, both of which reduce the nucleophilicity of H24 and are likely to be offset by positioning of a peptidyl-tRNA substrate. The region proximal to H24 and the lid region exhibit slow motions that may assist in accommodating the substrate. Helix α3 exhibits a slow wobble with intermediate time scale motions of its N-cap residue N118, which may work as a flypaper to position the scissile ester bond of the substrate. Overall, the dynamics of interactions between the side chains of N14, H24, D97, and N118, control the catalysis of substrate by this enzyme.

Functional Studies on Membrane Proteins by Means of H/D Exchange in Infrared: Structural Changes in Na+ NQR from V. cholerae in the Presence of Lipids

H/D exchange kinetics at the level of the amide proton in the mid infrared (1700-1500 cm^-1) make it possible to study the conformational flexibility of membrane proteins, independent of size or the presence of detergent or lipids. Slow, medium, and fast exchanging domains are distinguished, which reveal a different accessibility to the solvent. Whereas amide hydrogens undergo rapid exchange with solvent in an open structure, hydrogens experience much slower exchange when involved in H-bonded structures or when sterically inaccessible to the solvent. Here, we describe the protocol that was used to study the effect of phospholipids on the overall structure of the Na⁺ NQR from V. cholerae, a sodium pumping membrane protein.

LCP crystallization and X-ray diffraction analysis of VcmN, a MATE transporter from Vibrio cholerae

Multidrug and toxic compound extrusion (MATE) transporters, one of the multidrug exporter families, efflux xenobiotics towards the extracellular side of the membrane. Since MATE transporters expressed in bacterial pathogens contribute to multidrug resistance, they are important therapeutic targets. Here, a MATE-transporter homologue from Vibrio cholerae, VcmN, was overexpressed in Escherichia coli, purified and crystallized in lipidic cubic phase (LCP). X-ray diffraction data were collected to 2.5 Å resolution from a single crystal obtained in a sandwich plate. The crystal belonged to space group P212121, with unit-cell parameters a = 52.3, b = 93.7, c = 100.2 Å. As a result of further LCP crystallization trials, crystals of larger size were obtained using sitting-drop plates. X-ray diffraction data were collected to 2.2 Å resolution from a single crystal obtained in a sitting-drop plate. The crystal belonged to space group P212121, with unit-cell parameters a = 61.9, b = 91.8, c = 100.9 Å. The present work provides valuable insights into the atomic resolution structure determination of membrane transporters.

Toward increased concentration sensitivity for continuous wave EPR investigations of spin-labeled biological macromolecules at high fields

High-field, high-frequency electron paramagnetic resonance (EPR) spectroscopy at W-(∼94 GHz) and D-band (∼140 GHz) is important for investigating the conformational dynamics of flexible biological macromolecules because this frequency range has increased spectral sensitivity to nitroxide motion over the 100 ps to 2 ns regime. However, low concentration sensitivity remains a roadblock for studying aqueous samples at high magnetic fields. Here, we examine the sensitivity of a non-resonant thin-layer cylindrical sample holder, coupled to a quasi-optical induction-mode W-band EPR spectrometer (HiPER), for continuous wave (CW) EPR analyses of: (i) the aqueous nitroxide standard, TEMPO; (ii) the unstructured to α-helical transition of a model IDP protein; and (iii) the base-stacking transition in a kink-turn motif of a large 232 nt RNA. For sample volumes of ∼50 μL, concentration sensitivities of 2-20 μM were achieved, representing a ∼10-fold enhancement compared to a cylindrical TE011 resonator on a commercial Bruker W-band spectrometer. These results therefore highlight the sensitivity of the thin-layer sample holders employed in HiPER for spin-labeling studies of biological macromolecules at high fields, where applications can extend to other systems that are facilitated by the modest sample volumes and ease of sample loading and geometry.

Comparative sequence- and structure-inspired drug design for PilF protein of Neisseria meningitidis

Serogroup A of Neisseria meningitidis is the organism responsible for causing epidemic diseases in developing countries by a pilus-mediated adhesion to human brain endothelial cells. Type IV pilus assembly protein (PilF) associated with bacterial adhesion, aggregation, invasion, host cell signaling, surface motility, and natural transformation can be considered as a candidate for effective anti-meningococcal drug development. Since the crystal structure of PilF was not available, in the present study, it was modeled after the Z2491 strain (CAM09255.1) using crystal structure of chain A of Vibrio cholerae putative Ntpase EpsE (Protein Data Bank (PDB) ID: 1P9R) and then we based this analysis on sequence comparisons and structural similarity using in silico methods and docking processes, to design a suitable inhibitor molecule. The ligand 3-{(4S)-5-{[(1R)-1-cyclohexylethyl]amino}-4-[(5S)-5-(prop-2-en-1-yl) cyclopent-1-en-1-yl]-1,4-dihydro-7H-pyrrolo[2,3-d] pyrimidin-7-yl}-1,2-dideoxy-b-L-erythro-hex-1-en-3-ulofuranosyl binds to the protein with a binding energy of -8.10 kcal and showed a drug likeness of 0.952 with no predicted health hazard. It can be utilized as a potent inhibitor of N. meningitidis pilus-mediated adhesion to human brain endothelial cells preventing meningeal colonization.

Serine 26 in the PomB subunit of the flagellar motor is essential for hypermotility of Vibrio cholerae

Vibrio cholerae is motile by means of its single polar flagellum which is driven by the sodium-motive force. In the motor driving rotation of the flagellar filament, a stator complex consisting of subunits PomA and PomB converts the electrochemical sodium ion gradient into torque. Charged or polar residues within the membrane part of PomB could act as ligands for Na⁺, or stabilize a hydrogen bond network by interacting with water within the putative channel between PomA and PomB. By analyzing a large data set of individual tracks of swimming cells, we show that S26 located within the transmembrane helix of PomB is required to promote very fast swimming of V. cholerae. Loss of hypermotility was observed with the S26T variant of PomB at pH 7.0, but fast swimming was restored by decreasing the H⁺ concentration of the external medium. Our study identifies S26 as a second important residue besides D23 in the PomB channel. It is proposed that S26, together with D23 located in close proximity, is important to perturb the hydration shell of Na⁺ before its passage through a constriction within the stator channel.

Bottom-up and top-down solid-state NMR approaches for bacterial biofilm matrix composition

The genomics and proteomics revolutions have been enormously successful in providing crucial "parts lists" for biological systems. Yet, formidable challenges exist in generating complete descriptions of how the parts function and assemble into macromolecular complexes and whole-cell assemblies. Bacterial biofilms are complex multicellular bacterial communities protected by a slime-like extracellular matrix that confers protection to environmental stress and enhances resistance to antibiotics and host defenses. As a non-crystalline, insoluble, heterogeneous assembly, the biofilm extracellular matrix poses a challenge to compositional analysis by conventional methods. In this perspective, bottom-up and top-down solid-state NMR approaches are described for defining chemical composition in complex macrosystems. The "sum-of-the-parts" bottom-up approach was introduced to examine the amyloid-integrated biofilms formed by Escherichia coli and permitted the first determination of the composition of the intact extracellular matrix from a bacterial biofilm. An alternative top-down approach was developed to define composition in Vibrio cholerae biofilms and relied on an extensive panel of NMR measurements to tease out specific carbon pools from a single sample of the intact extracellular matrix. These two approaches are widely applicable to other heterogeneous assemblies. For bacterial biofilms, quantitative parameters of matrix composition are needed to understand how biofilms are assembled, to improve the development of biofilm inhibitors, and to dissect inhibitor modes of action. Solid-state NMR approaches will also be invaluable in obtaining parameters of matrix architecture.

Cholera toxin B: one subunit with many pharmaceutical applications

Cholera, a waterborne acute diarrheal disease caused by Vibrio cholerae, remains prevalent in underdeveloped countries and is a serious health threat to those living in unsanitary conditions. The major virulence factor is cholera toxin (CT), which consists of two subunits: the A subunit (CTA) and the B subunit (CTB). CTB is a 55 kD homopentameric, non-toxic protein binding to the GM1 ganglioside on mammalian cells with high affinity. Currently, recombinantly produced CTB is used as a component of an internationally licensed oral cholera vaccine, as the protein induces potent humoral immunity that can neutralize CT in the gut. Additionally, recent studies have revealed that CTB administration leads to the induction of anti-inflammatory mechanisms in vivo. This review will cover the potential of CTB as an immunomodulatory and anti-inflammatory agent. We will also summarize various recombinant expression systems available for recombinant CTB bioproduction.

Crystallization of two operator complexes from the Vibrio cholerae HigBA2 toxin-antitoxin module

The HigA2 antitoxin and the HigBA2 toxin-antitoxin complex from Vibrio cholerae were crystallized in complex with their operator box. Screening of 22 different DNA duplexes led to two crystal forms of HigA2 complexes and one crystal form of a HigBA2 complex. Crystals of HigA2 in complex with a 17 bp DNA duplex belong to space group P3221, with unit-cell parameters a = b = 94.0, c = 123.7 Å, and diffract to 2.3 Å resolution. The second form corresponding to HigA2 in complex with a 19 bp duplex belong to space group P43212 and only diffract to 3.45 Å resolution. Crystals of the HigBA2 toxin-antitoxin were obtained in complex with a 31 bp duplex and belonged to space group P41212, with unit-cell parameters a = b = 113.6, c = 121.1 Å. They diffract to 3.3 Å resolution.

Characterization of the Vibrio cholerae extracellular matrix: a top-down solid-state NMR approach

Bacterial biofilms are communities of bacterial cells surrounded by a self-secreted extracellular matrix. Biofilm formation by Vibrio cholerae, the human pathogen responsible for cholera, contributes to its environmental survival and infectivity. Important genetic and molecular requirements have been identified for V. cholerae biofilm formation, yet a compositional accounting of these parts in the intact biofilm or extracellular matrix has not been described. As insoluble and non-crystalline assemblies, determinations of biofilm composition pose a challenge to conventional biochemical and biophysical analyses. The V. cholerae extracellular matrix composition is particularly complex with several proteins, complex polysaccharides, and other biomolecules having been identified as matrix parts. We developed a new top-down solid-state NMR approach to spectroscopically assign and quantify the carbon pools of the intact V. cholerae extracellular matrix using ¹³C CPMAS and ¹³C{(¹⁵N}, ¹⁵N{³¹P}, and ¹³C{³¹P}REDOR. General sugar, lipid, and amino acid pools were first profiled and then further annotated and quantified as specific carbon types, including carbonyls, amides, glycyl carbons, and anomerics. In addition, ¹⁵N profiling revealed a large amine pool relative to amide contributions, reflecting the prevalence of molecular modifications with free amine groups. Our top-down approach could be implemented immediately to examine the extracellular matrix from mutant strains that might alter polysaccharide production or lipid release beyond the cell surface; or to monitor changes that may accompany environmental variations and stressors such as altered nutrient composition, oxidative stress or antibiotics. More generally, our analysis has demonstrated that solid-state NMR is a valuable tool to characterize complex biofilm systems.

Probing the size of proteins with glass nanopores

Single molecule studies using nanopores have gained attention due to the ability to sense single molecules in aqueous solution without the need to label them. In this study, short DNA molecules and proteins were detected with glass nanopores, whose sensitivity was enhanced by electron reshaping which decreased the nanopore diameter and created geometries with a reduced sensing length. Further, proteins having molecular weights (MW) ranging from 12 kDa to 480 kDa were detected, which showed that their corresponding current peak amplitude changes according to their MW. In the case of the 12 kDa ComEA protein, its DNA-binding properties to an 800 bp long DNA molecule was investigated. Moreover, the influence of the pH on the charge of the protein was demonstrated by showing a change in the translocation direction. This work emphasizes the wide spectrum of detectable molecules using nanopores from glass nanocapillaries, which stand out because of their inexpensive, lithography-free, and rapid manufacturing process.

Structural biochemistry of a Vibrio cholerae dinucleotide cyclase reveals cyclase activity regulation by folates

Cyclic dinucleotides are a newly expanded class of second messengers that contribute to the regulation of multiple different pathways in bacterial, eukaryotic, and archaeal cells. The recently identified Vibrio cholerae dinucleotide cyclase (DncV, the gene product of VC0179) can generate three different cyclic dinucleotides and preferentially synthesize a hybrid cyclic-GMP-AMP. Here, we report the crystal structural and functional studies of DncV. We unexpectedly observed a 5-methyltetrahydrofolate diglutamate (5MTHFGLU2) molecule bound in a surface pocket opposite the nucleotide substrate-binding groove of DncV. Subsequent mutagenesis and functional studies showed that the enzymatic activity of DncV is regulated by folate-like molecules, suggesting the existence of a signaling pathway that links folate-like metabolism cofactors to the regulation of cyclic dinucleotide second messenger synthesis. Sequence analysis showed that the residues involved in 5MTHFGLU2 binding are highly conserved in DncV orthologs, implying the presence of this regulation mechanism in a wide variety of bacteria.

On-chip detection of rolling circle amplified DNA molecules from Bacillus globigii spores and Vibrio cholerae

For the first time DNA coils formed by rolling circle amplification are quantified on-chip by Brownian relaxation measurements on magnetic nanobeads using a magnetoresistive sensor. No external magnetic fields are required besides the magnetic field arising from the current through the sensor, which makes the setup very compact. Limits of detection down to 500 Bacillus globigii spores and 2 pM of Vibrio cholerae are demonstrated, which are on the same order of magnitude or lower than those achieved previously using a commercial macro-scale AC susceptometer. The chip-based readout is an important step towards the realization of field tests based on rolling circle amplification molecular analyses.

Crystallization and preliminary analysis of the NqrA and NqrC subunits of the Na+-translocating NADH:ubiquinone oxidoreductase from Vibrio cholerae

The Na+-translocating NADH:ubiquinone oxidoreductase (Na+-NQR) from Vibrio cholerae is a membrane protein complex consisting of six different subunits NqrA-NqrF. The major domains of the NqrA and NqrC subunits were heterologously expressed in Escherichia coli and crystallized. The structure of NqrA1-377 was solved in space groups C222₁ and P2₁ by SAD phasing and molecular replacement at 1.9 and 2.1 Å resolution, respectively. NqrC devoid of the transmembrane helix was co-expressed with ApbE to insert the flavin mononucleotide group covalently attached to Thr225. The structure was determined by molecular replacement using apo-NqrC of Parabacteroides distasonis as search model at 1.8 Å resolution.

Functional and structural characterization of Vibrio cholerae extracellular serine protease B, VesB

The chymotrypsin subfamily A of serine proteases consists primarily of eukaryotic proteases, including only a few proteases of bacterial origin. VesB, a newly identified serine protease that is secreted by the type II secretion system in Vibrio cholerae, belongs to this subfamily. VesB is likely produced as a zymogen because sequence alignment with trypsinogen identified a putative cleavage site for activation and a catalytic triad, His-Asp-Ser. Using synthetic peptides, VesB efficiently cleaved a trypsin substrate, but not chymotrypsin and elastase substrates. The reversible serine protease inhibitor, benzamidine, inhibited VesB and served as an immobilized ligand for VesB affinity purification, further indicating its relationship with trypsin-like enzymes. Consistent with this family of serine proteases, N-terminal sequencing implied that the propeptide is removed in the secreted form of VesB. Separate mutagenesis of the activation site and catalytic serine rendered VesB inactive, confirming the importance of these features for activity, but not for secretion. Similar to trypsin but, in contrast to thrombin and other coagulation factors, Na(+) did not stimulate the activity of VesB, despite containing the Tyr(250) signature. The crystal structure of catalytically inactive pro-VesB revealed that the protease domain is structurally similar to trypsinogen. The C-terminal domain of VesB was found to adopt an immunoglobulin (Ig)-fold that is structurally homologous to Ig-folds of other extracellular Vibrio proteins. Possible roles of the Ig-fold domain in stability, substrate specificity, cell surface association, and type II secretion of VesB, the first bacterial multidomain trypsin-like protease with known structure, are discussed.

Crystallization of the HigBA2 toxin-antitoxin complex from Vibrio cholerae

The genome of Vibrio cholerae encodes two higBA toxin-antitoxin (TA) modules that are activated by amino-acid starvation. Here, the TA complex of the second module, higBA2, as well as the C-terminal domain of the corresponding HigA2 antitoxin, have been purified and crystallized. The HigBA2 complex crystallized in two crystal forms. Crystals of form I belonged to space group P2(1)2(1)2, with unit-cell parameters a = 129.0, b = 119.8, c = 33.4 Å, and diffracted to 3.0 Å resolution. The asymmetric unit is likely to contain a single complex consisting of two toxin monomers and one antitoxin dimer. The second crystal form crystallized in space group P3(2)21, with unit-cell parameters a = 134.5, c = 55.4 Å. These crystals diffracted to 2.2 Å resolution and probably contain a complex with a different stoichiometry. Crystals of the C-terminal domain of HigA2 belonged to space group C2, with unit-cell parameters a = 115.4, b = 61.2, c = 73.8 Å, β = 106.7°, and diffracted to 1.8 Å resolution.

[Serologic study of experimental cholera polymer antigen diagnosticums]

AIM

Evaluation of quality indicators of constructed cholera antigen polymer diagnosticums by using a complex of specific anti-cholera sera. MATERIALS AND METHODS. Cell lysates of cholera vibrio strains Vibrio cholerae cholerae 1395, V. eltor Ogawa 2044, V. eltor Inaba 13020, V. cholerae O139 16064 were sensitins for experimental preparations. 3 sera from cholera patients, normal human sera, cholera O1 (Ogawa, Inaba) commercial horse, cholera O139 commercial rabbit and heterologic sera against shigella, salmonella, escherichia and yersinia as well as experimental cholera rabbit sera against O1 and O139 were used as control.

RESULTS

The study established that diagnosticums based on V. cholerae cholerae 1395 and V. cholerae O139 16064 strain sensitins by quality indicators may be used in the future for construction of these diagnosticums.

CONCLUSION

Antibody containing preparations--commercial horse O1 sera, rabbit experimental and commercial sera and MCA O139 demonstrating titers not lower than 1/5120-1/10240 may serve as a control of experimental diagnosticums in the absence of human sera from cholera patients.

Structure of Vibrio cholerae ribosome hibernation promoting factor

The X-ray crystal structure of ribosome hibernation promoting factor (HPF) from Vibrio cholerae is presented at 2.0 Å resolution. The crystal was phased by two-wavelength MAD using cocrystallized cobalt. The asymmetric unit contained two molecules of HPF linked by four Co atoms. The metal-binding sites observed in the crystal are probably not related to biological function. The structure of HPF has a typical β-α-β-β-β-α fold consistent with previous structures of YfiA and HPF from Escherichia coli. Comparison of the new structure with that of HPF from E. coli bound to the Thermus thermophilus ribosome [Polikanov et al. (2012), Science, 336, 915-918] shows that no significant structural changes are induced in HPF by binding.

Modulation of quaternary structure and enhancement of ligand binding by the K-turn of tandem glycine riboswitches

Most known glycine riboswitches have two homologous aptamer domains arranged in tandem and separated by a short linker. The two aptamers associate through reciprocal "quaternary" interactions that have been proposed to result in cooperative glycine binding. Recently, the interaptamer linker was found to form helix P0 with a previously unrecognized segment 5' to the first aptamer domain. P0 was shown to increase glycine affinity, abolish cooperativity, and conform to the K-turn motif consensus. We examine the global thermodynamic and structural role of P0 using isothermal titration calorimetry (ITC) and small-angle X-ray scattering (SAXS), respectively. To evaluate the generality of P0 function, we prepared glycine riboswitch constructs lacking and including P0 from Bacillus subtilis, Fusobacterium nucleatum, and Vibrio cholerae. We find that P0 indeed folds into a K-turn, supports partial pre-folding of all three glycine-free RNAs, and is required for ITC observation of glycine binding under physiologic Mg(2+) concentrations. Except for the unusually small riboswitch from F. nucleatum, the K-turn is needed for maximally compacting the glycine-bound states of the RNAs. Formation of a ribonucleoprotein complex between the B. subtilis or the F. nucleatum RNA constructs and the bacterial K-turn binding protein YbxF promotes additional folding of the free riboswitch, and enhances glycine binding. Consistent with the previously reported loss of cooperativity, P0-containing B. subtilis and V. cholerae tandem aptamers bound no more than one glycine molecule per riboswitch. Our results indicate that the P0 K-turn helps organize the quaternary structure of tandem glycine riboswitches, thereby facilitating ligand binding under physiologic conditions.

Unique iron coordination in iron-chelating molecule vibriobactin helps Vibrio cholerae evade mammalian siderocalin-mediated immune response

Iron is essential for the survival of almost all bacteria. Vibrio cholerae acquires iron through the secretion of a catecholate siderophore called vibriobactin. At present, how vibriobactin chelates ferric ion remains controversial. In addition, the mechanisms underlying the recognition of ferric vibriobactin by the siderophore transport system and its delivery into the cytoplasm specifically have not been clarified. In this study, we report the high-resolution structures of the ferric vibriobactin periplasmic binding protein ViuP and its complex with ferric vibriobactin. The holo-ViuP structure reveals that ferric vibriobactin does not adopt the same iron coordination as that of other catecholate siderophores such as enterobactin. The three catechol moieties donate five, rather than six, oxygen atoms as iron ligands. The sixth iron ligand is provided by a nitrogen atom from the second oxazoline ring. This kind of iron coordination results in the protrusion of the second catechol moiety and renders the electrostatic surface potential of ferric vibriobactin less negatively polarized compared with ferric enterobactin. To accommodate ferric vibriobactin, ViuP has a deeper subpocket to hold the protrusion of the second catechol group. This structural characteristic has not been observed in other catecholate siderophore-binding proteins. Biochemical data show that siderocalin, which is part of the mammalian innate immune system, cannot efficiently sequester ferric vibriobactin in vitro, although it can capture many catecholate siderophores with high efficiency. Our findings suggest that the unique iron coordination found in ferric vibriobactin may be utilized by some pathogenic bacteria to evade the siderocalin-mediated innate immune response of mammals.

Crystal structure of a concentrative nucleoside transporter from Vibrio cholerae at 2.4 Å

Nucleosides are required for DNA and RNA synthesis, and the nucleoside adenosine has a function in a variety of signalling processes. Transport of nucleosides across cell membranes provides the major source of nucleosides in many cell types and is also responsible for the termination of adenosine signalling. As a result of their hydrophilic nature, nucleosides require a specialized class of integral membrane proteins, known as nucleoside transporters (NTs), for specific transport across cell membranes. In addition to nucleosides, NTs are important determinants for the transport of nucleoside-derived drugs across cell membranes. A wide range of nucleoside-derived drugs, including anticancer drugs (such as Ara-C and gemcitabine) and antiviral drugs (such as zidovudine and ribavirin), have been shown to depend, at least in part, on NTs for transport across cell membranes. Concentrative nucleoside transporters, members of the solute carrier transporter superfamily SLC28, use an ion gradient in the active transport of both nucleosides and nucleoside-derived drugs against their chemical gradients. The structural basis for selective ion-coupled nucleoside transport by concentrative nucleoside transporters is unknown. Here we present the crystal structure of a concentrative nucleoside transporter from Vibrio cholerae in complex with uridine at 2.4 Å. Our functional data show that, like its human orthologues, the transporter uses a sodium-ion gradient for nucleoside transport. The structure reveals the overall architecture of this class of transporter, unravels the molecular determinants for nucleoside and sodium binding, and provides a framework for understanding the mechanism of nucleoside and nucleoside drug transport across cell membranes.

[Cholera vibrios lectins as main pathogenicity and persistence factors (biotechnological aspects of use)]

Literature data and results of our studies of lectins are analyzed in the review. All the leading pathogenicity factors of cholera vibrios that possess enzymatic activity--cholera toxin, hemolysin, neuraminidase, chitinase have several lectin domains, that determine not only their pathogenetic role but also open perspectives for their use in medical practice. At the same time the variable receptor profile of cholera vibrios cells of various biovars and epidemical significance established with hemagglutination inhibition reaction by carbohydrates could be used to develop new principles of testing and typing of cholera vibrios.

Overexpression, purification, crystallization and preliminary X-ray analysis of CheY4 from Vibrio cholerae O395

Chemotaxis and motility greatly influence the infectivity of Vibrio cholerae, although the role of chemotaxis genes in V. cholerae pathogenesis is poorly understood. In contrast to the single copy of CheY found in Escherichia coli and Salmonella typhimurium, four CheYs (CheY1-CheY4) are present in V. cholerae. While insertional disruption of the cheY4 gene results in decreased motility, insertional duplication of this gene increases motility and causes enhanced expression of the two major virulence genes. Additionally, cheY3/cheY4 influences the activation of the transcription factor NF-κB, which triggers the generation of acute inflammatory responses. V. cholerae CheY4 was cloned, overexpressed and purified by Ni-NTA affinity chromatography followed by gel filtration. Crystals of CheY4 grown in space group C2 diffracted to 1.67 Å resolution, with unit-cell parameters a = 94.4, b = 31.9, c = 32.6 Å, β = 96.5°, whereas crystals grown in space group P3(2)21 diffracted to 1.9 Å resolution, with unit-cell parameters a = b = 56.104, c = 72.283 Å, γ = 120°.

Cloning, expression, purification, crystallization and preliminary X-ray analysis of the 31 kDa Vibrio cholerae heat-shock protein VcHsp31

The Gram-negative bacterium Vibrio cholerae, which is responsible for the diarrhoeal disease cholera in humans, induces the expression of numerous heat-shock genes. VcHsp31 is a 31 kDa putative heat-shock protein that belongs to the DJ-1/PfpI superfamily, functioning as both a chaperone and a protease. VcHsp31 has been cloned, overexpressed and purified by Ni(2+)-NTA affinity chromatography followed by gel filtration. Crystals of VcHsp31 were grown in the presence of PEG 6000 and MPD; they belonged to space group P2(1) and diffracted to 1.9 Å resolution. Assuming the presence of six molecules in the asymmetric unit, the Matthews coefficient was estimated to be 1.97 Å(3) Da(-1), corresponding to a solvent content of 37.4%.

Characterization of Cholix toxin-induced apoptosis in HeLa cells

Cholix toxin (Cholix) is a novel ADP-ribosylating cytotoxin produced by Vibrio cholerae, which utilizes eukaryotic elongation factor 2 as a substrate and acts by a mechanism similar to that of diphtheria toxin and Pseudomonas exotoxin A. First it was found that Cholix-treated HeLa cells exhibited caspase-dependent apoptosis, whereas intestinal cells such as Caco-2, HCT116, and RKO did not. Here we investigated Cholix-induced cell death signaling pathways in HeLa cells. Cholix-induced cytochrome c release into cytosol was initiated by specific conformational changes of pro-apoptotic Bak associated with Bax. Silencing of bak/bax genes or bak gene alone using siRNA significantly suppressed cytochrome c release and caspase-7 activation, but not activation of caspases-3 and -9. Although pretreatment with a caspase-8 inhibitor (Z-IETD-FMK) reduced Cholix-induced cytochrome c release and activation of caspases-3, -7, and -9, cytotoxicity was not decreased. Pretreatment with Z-YVAD-FMK, which inhibits caspase-1, -4, and -5, suppressed not only cytochrome c release, activation of caspase-3, -7, -8, or -9, and PARP cleavage, but also cytotoxicity, indicating that caspase-1, -4, and -5 activation is initiated at an early stage of Cholix-induced apoptosis and promotes caspase-8 activation. These results show that the inflammatory caspases (caspase-1, -4, and -5) and caspase-8 are responsible for both mitochondrial signals and other caspase activation. In conclusion, we showed that Cholix-induced caspase activation plays an essential role in generation of apoptotic signals, which are mediated by both mitochondria-dependent and -independent pathways.

Molecular cloning and characterization of mannitol-1-phosphate dehydrogenase from Vibrio cholerae

Vibrio cholerae utilizes mannitol through an operon of the phosphoenolpyruvate-dependent phosphotransferase (PTS) type. A gene, mtlD, encoding mannitol-1-phosphate dehydrogenase was identified within the 3.9 kb mannitol operon of V. cholerae. The mtlD gene was cloned from V. cholerae O395, and the recombinant enzyme was functionally expressed in E. coli as a 6×His-tagged protein and purified to homogeneity. The recombinant protein is a monomer with a molecular mass of 42.35 kDa. The purified recombinant MtlD reduced fructose 6-phosphate (F6P) using NADH as a cofactor with a K(m) of 1.54 +/- 0.1 mM and V(max) of 320.8 +/- 7.81 micronmol/min/mg protein. The pH and temperature optima for F6P reduction were determined to be 7.5 and 37°C, respectively. Using quantitative real-time PCR analysis, mtlD was found to be constitutively expressed in V. cholerae, but the expression was up-regulated when grown in the presence of mannitol. The MtlD expression levels were not significantly different between V. cholerae O1 and non-O1 strains.

[Sialic acids and O-acetyl groups as markers of biological activity of microbial polysaccharides in plague and cholera agents]

AIM

To determine sialic acids and O-acetyl groups content in Yersinia pestis and Vibrio cholerae antigens in order to establish their association with biological activity.

MATERIALS AND METHODS

The following antigens of Y. pestis EV NIIEG strain--capsular antigen (F1), major somatic antigen (MSA), lipopolysaccharide (LPS), Pla-protease, allergen pestin PP--as well as O-antigens (O-AG) of V. cholerae serogroups O1 and O139 were used in the study. Sialic acids were identified by the thiobarbituric method, and O-acetyl groups--according to Alicino. Specific polysaccharides in the MSA and O-antigens were detected by the immunodiffusion assay.

RESULTS

Sialic acids were found in LPS, Pla-protease, allergen pestin PP, and all cholera O-AG; their absence was demonstrated in MSA and F1. O-acetyl groups were identified in cholera O-AG of both studied serogroups as well as in LPS, Pla-protease, MSA and pestin PP of Y. pestis. Tendency to correlation between O-acetyl groups content in MSA and serological activity titer was observed.

CONCLUSION

Sialic acids and O-acetyl groups identified in carbohydrate-containing antigens of Y. pestis and V. cholerae could be characterized as reaction-active markers of pathogenetic mechanisms of cholera and plague infections as well as immunochemical activity of microbial polysaccharides.

Cholera- and anthrax-like toxins are among several new ADP-ribosyltransferases

Chelt, a cholera-like toxin from Vibrio cholerae, and Certhrax, an anthrax-like toxin from Bacillus cereus, are among six new bacterial protein toxins we identified and characterized using in silico and cell-based techniques. We also uncovered medically relevant toxins from Mycobacterium avium and Enterococcus faecalis. We found agriculturally relevant toxins in Photorhabdus luminescens and Vibrio splendidus. These toxins belong to the ADP-ribosyltransferase family that has conserved structure despite low sequence identity. Therefore, our search for new toxins combined fold recognition with rules for filtering sequences--including a primary sequence pattern--to reduce reliance on sequence identity and identify toxins using structure. We used computers to build models and analyzed each new toxin to understand features including: structure, secretion, cell entry, activation, NAD+ substrate binding, intracellular target binding and the reaction mechanism. We confirmed activity using a yeast growth test. In this era where an expanding protein structure library complements abundant protein sequence data--and we need high-throughput validation--our approach provides insight into the newest toxin ADP-ribosyltransferases.

Structure of a cation-bound multidrug and toxic compound extrusion transporter

Transporter proteins from the MATE (multidrug and toxic compound extrusion) family are vital in metabolite transport in plants, directly affecting crop yields worldwide. MATE transporters also mediate multiple-drug resistance (MDR) in bacteria and mammals, modulating the efficacy of many pharmaceutical drugs used in the treatment of a variety of diseases. MATE transporters couple substrate transport to electrochemical gradients and are the only remaining class of MDR transporters whose structure has not been determined. Here we report the X-ray structure of the MATE transporter NorM from Vibrio cholerae determined to 3.65 Å, revealing an outward-facing conformation with two portals open to the outer leaflet of the membrane and a unique topology of the predicted 12 transmembrane helices distinct from any other known MDR transporter. We also report a cation-binding site in close proximity to residues previously deemed critical for transport. This conformation probably represents a stage of the transport cycle with high affinity for monovalent cations and low affinity for substrates.

Cytotoxicity of Vibrio cholerae on Madin Darby Bovine Kidney cells

The cytotoxicity of cell-free culture filtrates of 31 isolates of Vibrio cholerae O1 and O139, 5 reference strains and 26 clinical isolates, was tested on Madin Darby Bovine Kidney (MDBK) cells and Vero cells. The 3-[4,5-dimethylthiazol-2-y]-2, 5-diphenyltetrazolium bromide (MTT) test was used to detect the effect of the filtrates on the proliferation and viability of cultured cell populations. The filtrates were prepared from serial ten-fold dilutions of inoculated AKI and APW broth media with and without the addition of polymyxin B. The APW culture filtrates of both V. cholerae O1 and O139 with and without added polymyxin B showed greater toxicity to MDBK cells as compared to AKI filtrates. The cytotoxicity of AKI-grown V. cholerae O139 to MDBK cells was greater than that of V. cholerae O1 grown in the same medium. The cytotoxicity of APW filtrates on Vero cells was low and only noted when polymyxin was added to the medium.

Cloning, overexpression, purification, crystallization and preliminary X-ray analysis of CheY3, a response regulator that directly interacts with the flagellar 'switch complex' in Vibrio cholerae

Vibrio cholerae is the aetiological agent of the severe diarrhoeal disease cholera. This highly motile organism uses the processes of motility and chemotaxis to travel and colonize the intestinal epithelium. Chemotaxis in V. cholerae is far more complex than that in Escherichia coli or Salmonella typhimurium, with multiple paralogues of various chemotaxis genes. In contrast to the single copy of the chemotaxis response-regulator protein CheY in E. coli, V. cholerae contains four CheYs (CheY1-CheY4), of which CheY3 is primarily responsible for interacting with the flagellar motor protein FliM, which is one of the major constituents of the ;switch complex' in the flagellar motor. This interaction is the key step that controls flagellar rotation in response to environmental stimuli. CheY3 has been cloned, overexpressed and purified by Ni-NTA affinity chromatography followed by gel filtration. Crystals of CheY3 were grown in space group R3, with a calculated Matthews coefficient of 2.33 A3 Da(-1) (47% solvent content) assuming the presence of one molecule per asymmetric unit.

A functional carbohydrate chip platform for analysis of carbohydrate-protein interaction

A carbohydrate chip based on glass or other transparent surfaces has been suggested as a potential tool for high-throughput analysis of carbohydrate-protein interactions. Here we proposed a facile, efficient, and cost-effective method whereby diverse carbohydrate types are modified in a single step and directly immobilized onto a glass surface, with retention of functional orientation. We modified various types of carbohydrates by reductive amination, in which reducing sugar groups were coupled with 4-(2-aminoethyl)aniline, which has di-amine groups at both ends. The modified carbohydrates were covalently attached to an amino-reactive NHS-activated glass surface by formation of stable amide bonds. This proposed method was applied for efficient construction of a carbohydrate microarray to analyze carbohydrate-protein interactions. The carbohydrate chip prepared using our method can be successfully used in diverse biomimetic studies of carbohydrates, including carbohydrate-biomolecule interactions, and carbohydrate sensor chip or microarray development for diagnosis and screening.

Comparison between a TaqMan polymerase chain reaction assay and a culture method for ctx-positive Vibrio cholerae detection

The main objective of the present work was to evaluate a real-time polymerase chain reaction (PCR) method to detect toxigenic Vibrio cholerae in Pangasius hypophthalmus, a freshwater fish cultured mainly in South East Asia. A FDA traditional culture method and a real-time PCR method of the ctx gene were used for detection of V. cholerae in spiked samples of pangasius fish. After an overnight enrichment of samples at 37 degrees C in alkaline peptone water, 2 cfu/25 g of fish was detected with both methods. Although both methods were very sensitive, obtaining results with culture methods may take several days, while real-time PCR takes only a few hours. Furthermore, with traditional methods, complementary techniques such as serotyping, although not available for all serogroups, are needed to identify toxigenic V. cholerae. However, with real-time PCR, toxigenic serogroups are detected in only one step after overnight enrichment.

Cholesterol specificity of some heptameric beta-barrel pore-forming bacterial toxins: structural and functional aspects

Apart from the thiol-specific/cholesterol-dependent cytolysin family of toxins (see Chapter 20) there are a number of other unrelated bacterial toxins that also have an affinity for plasma membrane cholesterol. Emphasis is given here on the Vibrio cholerae cytolysin (VCC) and the cytolysins from related Vibrio species. The inhibition of the cytolytic activity of these toxins by prior incubation with extracellular cholesterol or low density lipoprotein emerges as a unifying feature, as does plasma membrane cholesterol depletion. Incubation of VCC with cholesterol produces a heptameric oligomer, which is not equivalent to the pre-pore since it is unable to penetrate the plasma membrane. In structural terms, the precise sequence of VCC monomer binding to membrane, oligomer formation and pore insertion through the bilayer has yet to be fully defined. Several other bacterial toxins have a dependency for cholesterol, although the available data is limited in most cases.

Cholera toxin: A paradigm for multi-functional engagement of cellular mechanisms (Review)

Cholera toxin (Ctx) from Vibrio cholerae and its closely related homologue, heat-labile enterotoxin (Etx) from Escherichia coli have become superb tools for illuminating pathways of cellular trafficking and immune cell function. These bacterial protein toxins should be viewed as conglomerates of highly evolved, multi-functional elements equipped to engage the trafficking and signalling machineries of cells. Ctx and Etx are members of a larger family of A-B toxins of bacterial (and plant) origin that are comprised of structurally and functionally distinct enzymatically active A and receptor-binding B sub-units or domains. Intoxication of mammalian cells by Ctx and Etx involves B pentamer-mediated receptor binding and entry into a vesicular pathway, followed by translocation of the enzymatic A1 domain of the A sub-unit into the target cell cytosol, where covalent modification of intracellular targets leads to activation of adenylate cyclase and a sequence of events culminating in life-threatening diarrhoeal disease. Importantly, Ctx and Etx also have the capacity to induce a wide spectrum of remarkable immunological processes. With respect to the latter, it has been found that these toxins activate signalling pathways that modulate the immune system. This review explores the complexities of the cellular interactions that are engaged by these bacterial protein toxins, and highlights some of the new insights to have recently emerged.